1. Field of the Invention
The present invention relates to the manufacture of corrugated paper board and, specifically, to the belts used on corrugator machines, where corrugated paper board is manufactured. More specifically, the present invention is a seam for joining a corrugator belt into endless form on a corrugator machine.
2. Description of the Prior Art
The manufacture of corrugated paper board, or box board, on corrugator machines is well-known in the art. On such machines, corrugator belts pull a web of corrugated paper board first through a heating zone, where an adhesive used to bond layers of the web together is dried or cured, and then through a cooling zone. Frictional forces between the corrugator belt, specifically its so-called board side which contacts the web, and the web are primarily responsible for pulling the latter through the machine.
Corrugator belts are required to be strong and durable, and to have good dimensional stability under the tension and high-temperature conditions encountered on a corrugator machine. The belts must also be comparatively flexible in the longitudinal, or machine, direction, while having sufficient rigidity in the cross-machine direction, so that they may be guided and driven around their endless paths on the machine. Traditionally, it has also been desirable for the belts to have a porosity sufficient to permit vapor to pass freely through them, but to be sufficiently incompatible with the moisture in the vapor to avoid their adsorption of condensed vapor, which could wet the surface of the corrugated paper board being manufactured.
As implied in the preceding paragraph, a corrugator belt takes the form of an endless loop when operating on a corrugator machine. In such form, the corrugator belt has a board side, as previously mentioned, and a back side, which is the inside of the endless loop. Frictional forces between the surface of the back side and the drive rolls of the corrugator machine move the corrugator belt, and frictional forces between the surface of the board side and the web of corrugated paper board pull the web through the machine.
Corrugator belts are generally flat-woven, multilayered fabrics, which are produced in lengths and widths appropriate for the corrugator machines on which they are to be installed. The ends of the fabrics are provided with seaming means, so that they may be joined to one another with a lacing cable when the corrugator belt is being installed on a corrugator machine.
One of the most common seams used for corrugator belts is the so-called clipper seam. This variety of seam comprises a plurality of generally U-shaped clipper hooks, which are installed in an alternating relationship on the ends of the corrugator belt, so that, when the two ends of the corrugator belt are brought together, they may be interdigitated to define a passage through which a lacing cable or pintle may be directed to secure one end to the other. The individual clipper hooks are of stiff metal wire, and have two parallel members, the upright portions of their xe2x80x9cUxe2x80x9d shapes, which are separated from one another by an amount substantially equal to, or slightly less than, the thickness of the corrugator belt, and which have mutually directed barbs, so that, when pushed onto the end of the corrugator belt, they are not readily removed. The two parallel members, which are on opposite sides of an end of the corrugator belt after the clipper hook has been installed, and which lie snugly against the opposite surfaces thereof, may be of equal or different length, and may therefor extend the same or different amounts longitudinally from the end of the corrugator belt.
In a typical corrugator machine, the heating zone comprises a series of hot plates across which the web of corrugated paper board is pulled by the corrugator belt. A plurality of weighted rollers or, alternatively, one or more air plenums within the endless loop formed by the corrugator belt, force the corrugator belt toward the hot plates, so that the corrugator belt may, in turn, press the corrugated paper board against the hot plates and generate frictional forces sufficient to pull the corrugated paper board thereacross. The same or similar means are also used in the cooling zone of the corrugator machine.
Unfortunately, the applied forces required for the corrugator belt to pull the corrugated paper board through the machine may cause the clipper seams to leave objectionable marks on the board or, even worse, may cause the seam to tear or break the board, leading to shutdowns and lost production.
One approach toward solving this problem has been to provide a protective flap to cover the clipper seam on the board side of the corrugator belt. Such a flap may be provided by slicing the ends of the corrugator belt in a plane parallel to the surfaces of the belt to form two plies. Then, approximately equal lengths of the board-side ply at one end and of the back-side ply at the other end are removed, giving each end a steplike appearance. A clipper seam is then formed using the back-side plies, and, because of the steplike overlap of the ends, is covered by a flap on the board side. The flap, of course, may require trimming to fit into the space produced when the corresponding length of board-side ply was removed from the other end. When the belt is installed on the corrugator machine, the flap is oriented in a direction opposite to that in which the belt will run on the machine.
While flaps produced in this manner do indeed reduce the marking of the board by the clipper seam, they gradually deteriorate during the running life of the belt, becoming worn and unraveling along their trailing edges to the point where, in the worst situations, the clipper seam is exposed and can mark the corrugated paper board.
The present invention is intended to overcome these problems experienced with the clipper seams of the prior art.
Accordingly, the present invention is a corrugator belt having a clipper seam which includes compressible material to prevent the individual clipper hooks making up the clipper seam from coming into firm contact with the corrugated paper board being manufactured on a corrugator machine.
More specifically, the present corrugator belt comprises a base having a first end and a second end, and a first side and a second side. A plurality of clipper hooks is attached to the base at each of the first and second ends, and are used to join the first and second ends to one another with a clipper seam to place the corrugator belt into the form of an endless loop. A compressible material is at each of said first and second ends between adjacent ones of said plurality of clipper hooks on at least one of the first and second sides of the base to prevent a corrugated paper board from being marked or damaged by the clipper seam. The compressible material may take the form of a strip which wraps around each end from the first side to the second side beneath the clipper hooks. The compressible material, as a consequence, protrudes between adjacent ones of the plurality of clipper hooks at each of the first and second ends to prevent a corrugated paper board from firmly contacting the clipper hooks and being marked or otherwise damaged by them.
The present invention will now be described in more complete detail with frequent reference being made to the figures identified immediately below.